Dense finFET SRAM

ABSTRACT

A method for fabricating the device includes patterning a first structure and a second structure on a semiconductor device. A first angled ion implantation is applied to the second structure such that the first structure is protected and a second angled ion implantation is applied to the first structure such that the second structure is protected, wherein exposed portions of the first and second structures have an altered rate of oxidation. Oxidation is performed to form thicker or thinner oxide portions on the exposed portions of the first and second structures relative to unexposed portions of the first and second structures. Oxide portions are removed to an underlying layer of the first and second structures. The first and second structures are removed. Spacers are formed about a periphery of remaining oxide portions. The remaining oxide portions are removed. A layer below the spacers is patterned to form integrated circuit features.

RELATED APPLICATION INFORMATION

This application is a Continuation application of copending U.S. patentapplication Ser. No. 13/681,761 filed on Nov. 20, 2012, incorporatedherein by reference in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to integrated circuit processing, and moreparticularly to dense fin field effect transistor static random-accessmemory.

2. Description of the Related Art

FinFETs (fin field effect transistors) have become a viable devicearchitecture for 22 nm nodes and beyond. However, the formation offinFET SRAM (static random-access memory) and finFET logic pose newchallenges. One challenge is that some devices (e.g., logic FETs,multiple-finger pull down FETs/pass gate FETs) require epitaxy and amerged source/drain region while other devices (e.g., pull up FETs) onlyrequire epitaxy over the source/drain region, without the merging.Conventionally, dummy fins are utilized to accommodate the merge/unmergeissue. Unfortunately, dummy fins result a number of problems, such as anincrease in SRAM cell size and tight overlay control in fin patterning(removing dummy fin).

For 10 nm nodes, there is no known solution for forming SRAM finFETswith fin pitch below 20 nm due to the lack of known patterningtechniques to meet the tight overlay requirement.

SUMMARY

A method for fabricating a semiconductor device includes patterning afirst structure and a second structure on a semiconductor device. Afirst angled ion implantation is applied to the second structure suchthat the first structure is protected and a second angled ionimplantation is applied to the first structure such that the secondstructure is protected, wherein exposed portions of the first and secondstructures have an altered rate of oxidation. Oxidation is performed toform thicker or thinner oxide portions on the exposed portions of thefirst and second structures relative to unexposed portions of the firstand second structures. Oxide portions are removed to an underlying layerof the first and second structures. The first and second structures areremoved. Spacers are formed about a periphery of remaining oxideportions. The remaining oxide portions are removed. A layer below thespacers is patterned to form integrated circuit features.

A method for fabricating a semiconductor device includes patterning afirst mandrel structure and a second mandrel structure on asemiconductor device. A first angled ion implantation is applied to thesecond mandrel structure such that the first mandrel structure isprotected and a second angled ion implantation is applied to the firstmandrel structure such that the second mandrel structure is protected,wherein exposed portions of the first and second mandrel structures havean enhanced rate of oxidation. Oxidation is performed to form thickoxide portions on the exposed portions of the first and second mandrelstructures relative to unexposed portions of the first and secondmandrel structures. Oxide portions are removed to an underlying layer ofthe first and second mandrel structures. The first and second mandrelstructures are removed. Spacers are formed about a periphery ofremaining oxide portions. The remaining oxide portions are removed. Alayer below the spacers is patterned to form integrated circuitfeatures.

A semiconductor device includes a plurality of fins formed on asemiconductor substrate having a plurality of pitches. A plurality ofdevices are formed across two or more of the plurality of fins. Theplurality of devices include a first device including merged fins and asecond device including unmerged fins.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view of a semiconductor structure includinga substrate with a hardmask formed thereon, in accordance with oneillustrative embodiment;

FIG. 2 is a cross-sectional view of the structure patterned to formmandrels, in accordance with the present principles;

FIG. 3 is a cross-sectional view of the structure of FIG. 2 havingportions of a select mandrel bombarded in select portions using angledion implantation, in accordance with one illustrative embodiment;

FIG. 4 is a cross sectional view of the structure of FIG. 3 havingportions of a select mandrel bombarded in select portions using angledion implantation, in accordance with one illustrative embodiment;

FIG. 5 is a cross-sectional view of the resulting structure of FIG. 4after the block mask is removed, in accordance with one illustrativeembodiment;

FIG. 6 is a cross-sectional view of the structure of FIG. 5 afteroxidation is performed to provide thin oxide portions and thick oxideportions, in accordance with one illustrative embodiment;

FIG. 7 is a cross-sectional view of the structure of FIG. 6 having oxideportions removed to the underlying mandrel layer and having the mandrellayer removed, in accordance with one illustrative embodiment;

FIG. 8 is a cross-sectional view of the structure of FIG. 7 havingspacers formed about a periphery of the remaining oxide portions, inaccordance with one illustrative embodiment;

FIG. 9 is a cross-sectional view of the structure of FIG. 8 having theremaining oxide portions removed, in accordance with one illustrativeembodiment;

FIG. 10A is a top view of the structure of FIG. 9 having spacersemployed as a mask to form fins, in accordance with one illustrativeembodiment;

FIG. 10B is a cross-sectional view of the structure of FIG. 10A, inaccordance with one illustrative embodiment;

FIG. 11A is a top view of the structure of FIG. 10A having select finscut, in accordance with one illustrative embodiment;

FIG. 11B is a cross-section view of the structure of FIG. 10B havingselect fins cut, in accordance with one illustrative embodiment;

FIG. 12 is a top view of the structure of FIG. 11A after gate formation,in accordance with one illustrative embodiment;

FIG. 13 is a cross-sectional view of fins provided by the presentprinciples exemplary depicting fin pitch, in accordance with oneillustrative embodiment; and

FIG. 14 is a block/flow diagram showing a method for fabrication of asemiconductor device, in accordance with one illustrative embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with the present principles, a method and device areprovided for a dense finFET (fin field effect transistor) SRAM (staticrandom-access memory). Using angled ion implantation into selectportions of mandrels, the oxidation rate may be altered. For example,the implanted species may include fluorine to enhance the oxidation rateof exposed portions, or nitrogen to reduce the oxidation rate of exposedportions. Other ion types are also contemplated. Next, oxidation isperformed to form thick oxide and thin oxide, according to the implantedion type. A top layer of the oxidized portions are removed to theunderlying mandrel layers, and then the mandrels are removed. Spacersare formed around the remaining oxidized portions and the remainingoxidized portions are removed. The spacers are employed as a mask toform fins. Advantageously, the present principles provide fins with adense fin pitch which enables both merged fins and unmerged fins withoutthe use of dummy fins, eliminating the problems associated with dummyfins.

It is to be understood that the present invention will be described interms of a given illustrative architecture having a wafer; however,other architectures, structures, substrate materials and processfeatures and steps may be varied within the scope of the presentinvention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

A design for an integrated circuit chip may be created in a graphicalcomputer programming language, and stored in a computer storage medium(such as a disk, tape, physical hard drive, or virtual hard drive suchas in a storage access network). If the designer does not fabricatechips or the photolithographic masks used to fabricate chips, thedesigner may transmit the resulting design by physical means (e.g., byproviding a copy of the storage medium storing the design) orelectronically (e.g., through the Internet) to such entities, directlyor indirectly. The stored design is then converted into the appropriateformat (e.g., GDSII) for the fabrication of photolithographic masks,which typically include multiple copies of the chip design in questionthat are to be formed on a wafer. The photolithographic masks areutilized to define areas of the wafer (and/or the layers thereon) to beetched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a semiconductor substrate10 is shown having a mask formed thereon. The mask may include ahardmask, such as, e.g., amorphous silicon 14 on silicon nitride 12.Substrate 10 may include a semiconductor-on-insulator substrate (SOI),bulk substrate, etc. It should be understood that the substrate 10 mayinclude any material and is not limited to SOI or bulk materials. Forexample, substrate 10 may include Gallium Arsenide, monocrystallinesilicon, Germanium or any other material or combination of materials. Insome embodiments, the substrate 10 further comprises other features orstructures that are formed on or in the semiconductor substrate inprevious process steps.

Referring to FIG. 2, the structure of FIG. 1 is processed to formamorphous silicon mandrels 16, 18 and 20. Amorphous silicon layer 14 ispatterned, preferably using a lithographic process that may include aresist layer (not shown) and lithographic patterning. It is noted thatthe structure is not limited to mandrels 16, 18 and 20, but may includeany number of mandrels.

Referring to FIG. 3, a block mask 22 is applied over mandrels 16 and 18.The mask 22 preferably includes a photoresist mask. Mask 22 may beformed by a deposition process and preferably include an oxide, such assilicon dioxide, or a form thereof.

Angled ion implantation 26 is applied to one sidewall and the top ofmandrel 20 to form implanted portions 24 of mandrel 20. Angled ionimplantation 26 includes bombarding the mask 22 and mandrel 20 withions, such as, e.g., fluorine and/or nitrogen, at angles ofapproximately 1 degree to about 45 degrees with respect to a verticalnormal to a major surface of the device. Other angles of attack are alsocontemplated. Implant dose and energy may be selected according toimplant species. In one embodiment, nitrogen, for example, may beimplanted with an implant dose range of, e.g., 10¹²/cm² to 10¹⁴/cm², andthe implant energy can range from, e.g., 5 keV to 50 keV. In anotherembodiment, fluorine, for example, may be implanted with an implant doserange of, e.g., 1E14/cm² to 5E14/cm², and the implant energy can rangefrom, e.g., 1 keV to 50 keV. Other implant dosages and energies are alsocontemplated.

The implanted species will either enhance oxidation rate (e.g.,fluorine) or reduce oxidation rate (e.g., nitrogen). It is noted that anangled implantation is employed to be able to select which portions ofthe mandrel 20 are bombarded. Other surfaces are to be protected fromthe bombardment to ensure that selective surfaces are damaged by thebombardment while other surfaces are not. In one embodiment, one portionof a mandrel(s) may be implanted with, e.g., nitrogen while anotherportion of a mandrel(s) may be implanted with, e.g., fluorine. Otherembodiments are also contemplated.

Referring to FIG. 4, block mask 22 is removed (e.g., resist strip) and a(e.g., photoresist) block mask 28 is applied over mandrels 18 and 20. Asecond angled ion implantation 32 is applied to bombard a sidewall andtop of the mandrel 16 with ions, such as, e.g., fluorine and/ornitrogen, to form implanted portions 28 of mandrel 26. Block mask 28 isthen removed (e.g., resist strip).

Referring to FIG. 5, a resulting structure is shown including implantedportions 24 and 30 of mandrels 16 and 20, respectively. In thisexemplary embodiment, implanted portions 24 and 30 are implanted withfluorine to enhance the oxidation rate. However, it is noted thatimplanted portions 24 and 30 may also be implanted with nitrogen toreduce the oxidation rate. It should also be understood that the presentprinciples are not limited to implanting fluorine and/or nitrogen, butrather, the implanted portions 24 and 30 may be implanted with any typeof ion that will change the rate of oxidation.

It should further be understood that the resulting structure is notlimited to implanted portions 24 and 30 of mandrels 16 and 20,respectively. Rather, any number of angled ion implantations may beperformed, including any number of hard marks configured over one ormore mandrels, to provide one or more implanted portions within one ormore mandrels.

Referring to FIG. 6, oxidation is performed to form oxide portions 38 onmandrels 16, 18 and 20, including thick oxide portions 36 from fluorineimplanted portions 24 and 30, and thin oxide portions 34 fromunimplanted portions of the mandrel. It is noted that in someembodiments, where implanted portions 24 and 30 are implanted withnitrogen or other ions to reduce the oxidation rate, oxidation resultsin thinner oxide portions for nitrogen implanted portions and thickeroxide portions for unimplanted portions of the mandrel (not shown).

Referring to FIG. 7, oxide portions 38 are etched using known etchmethods, preferably to the underlying amorphous silicon layer of themandrels 16, 18 and 20. Etching preferably includes reactive ionetching, however other forms of etching are also contemplated (e.g., wetchemical etch method, dry plasma etch method, combinations of wetchemical etch methods and dry plasma etch methods, etc.). The amorphoussilicon (e.g., mandrels 16, 18 and 20) are then selectively etched(e.g., dry etch using hydrogen bromide, wet etch using potassiumhydroxide, etc.). The resulting structure is depicted in FIG. 7including remaining oxide portions 40.

It should be understood that the present principles are not limited tothe asymmetric oxidation approached discussed herein. Rather, othertechniques can be used for forming the mandrels with varying widths. Forexample, spacer deposition by angled ion implantation/etching, etc. maybe employed. Other techniques are also contemplated.

Referring to FIG. 8, processing continues to form spacers 42 about aperiphery of remaining oxide portions 40. The spacers may include anitride material, for example. The spacer material may be conformallydeposited over nitride layer 12.

Referring to FIG. 9, oxide portions 40 are selectively etched usingknown etching methods, such as, e.g., reactive ion etching. Referring toFIGS. 10A and 10B, fin structures are formed. FIG. 10A shows a top viewof the structure after fins 44 are formed. FIG. 10B is a cross-sectionalview of the structure after fins 44 are formed. Spacers 42 can beselectively etched to expose nitride layer 12. In one embodiment,spacers 42 are employed as a mask to etch through layer 12 and, at leastin part, layer 10 to form fins 44. In an alternate embodiment, spacers42 are removed after etching through layer 12, and layer 12 is employedas an etch mask to etch, at least in part, layer 10.

Referring to FIGS. 11A and 11B, the structure is shown after fin cut.FIG. 11A shows a top view of the structure after fins 44 are cut. FIG.11B shows a cross-sectional view of the structure after fins 44 are cut.Processing may continue as is known in the art.

Referring to FIG. 12, a top view of the structure is shown after gateformation in accordance with one exemplary embodiment, including firstand second SRAM (static random-access memory) cells 46 and 48,respectively. SRAM cells 46 and 48 include gates 50 formed across anumber of fins 44. First SRAM cell 46 includes narrow fin gap 52 withmerged source/drain epitaxy. Sources and drains of adjacent fins aremerged together during, e.g., the S/D epitaxy process to provide mergedfins. First SRAM cell 46 also includes wide fin gap 54 with unmergedsource/drain epitaxy. Second SRAM cell 48 includes pass gate devices 56with merged source/drain epitaxy, pull down devices 60 with mergedsource/drain epitaxy, and pull up devices 58 with unmerged source/drainepitaxy.

Referring to FIG. 13, an exemplary fin pitch for 10 nm SRAM isillustratively depicted, in accordance with one embodiment. Fins 44 havea width of 8 nm. Narrow fin gaps 62 have a pitch of 20 nm. Wide fin gaps64 have a pitch of 30 nm. In accordance with the present principles, adenser structure is provided than conventional 10 nm SRAM designs.Advantageously, dummy fins are not utilized, thereby eliminating allproblems associated with dummy fins. In addition, a relaxed overlaycontrol is provided.

Referring to FIG. 14, a block/flow diagram for a method for fabricationof features in integrated circuits is illustratively depicted inaccordance with a preferred embodiment. In block 102, structures arepatterned on a surface of a semiconductor device. The surface mayinclude a semiconductor substrate and may further include a hardmask,such as amorphous silicon over silicon nitride. The surface may furtherinclude other features on a semiconductor substrate formed in previousprocess steps. The structures preferably include first and secondmandrels, which may be formed from amorphous silicon or other suitablematerial. The mandrels may be patterned using a lithographic method.

In block 104, a first mask is formed over a first structure. The firstmask may include, e.g., a photoresist mask. In block 106, a first angledion implantation is applied such that the first structure is protectedby the mask and the second structure is unprotected. Exposed portions ofthe second structure have an altered oxidation rate relative tounexposed portions. In block 108, the angled ion implantation mayinclude selecting an angle of attack, direction of ion implantation andtype of ions to be implanted to modify the oxidation rate of exposedportions of the second structure. Preferably, the exposed portionsinclude the top and sidewall portions of the second structure. In oneembodiment, the first angled ion implantation is applied to implantfluorine to enhance the oxidation rate. In another embodiment, the firstangled ion implantation is applied to implant nitrogen to reduce theoxidation rate. Other types of ions to alter the oxidation rate ofexposed portions of the second structure are also contemplated. Thefirst mask is then removed.

In block 110, a second (e.g., photoresist) mask is formed over thesecond structure. In block 112, a second angled ion implantation isapplied such that the second structure is protected by the mask and thefirst structure is unprotected. Exposed portions of the first structurehave an altered oxidation rate relative to unexposed portions. In block114, the angled ion implantation may include selecting an angle ofattack, direction of ion implantation and type of ions to be implantedto modify the oxidation rate of exposed portions of the first structure.Preferably, the exposed portions include the top and sidewall of thefirst structure. In one embodiment, the second angled ion implantationis applied to implant fluorine to enhance the oxidation rate. In anotherembodiment, the second angled ion implantation is applied to implantnitrogen to reduce the oxidation rate. Other types of ions to alter theoxidation rate of exposed portions of the first structure are alsocontemplated. The second mask is then removed.

It should be understood that the first and second structures may beimplanted with different types of ions such that the exposed portions ofthe first and second structures have different oxidation rates.

In block 116, oxidation is performed. Exposed portions implanted withions to enhance oxidation rate (e.g., fluorine) forms thick oxiderelative to portions that are unexposed or implanted with ions to reducethe oxidation rate (e.g., nitrogen). Exposed portions implanted withions to reduce oxidation rate (e.g., nitrogen) forms thin oxide relativeto portions that are unexposed or implanted with ions to enhance theoxidation rate (e.g., fluorine).

In block 118, oxide portions are removed to the underlying (e.g., firstand second) structures. Oxide portions may be removed by applying areactive ion etching or other techniques as is known. In block 120, thestructures are selectively removed. In block 122, spacers are formedabout a periphery of the remaining oxide portions. The spacers includesidewall spacers and may be formed from a silicon nitride (nitride) orsimilar material. Since the oxide portions were formed thinner orthicker according to ion type, spacers of varying widths are provided.

In block 124, the remaining oxide portions are removed. This mayinvolve, e.g., RIE. In block 126, the spacers are employed as a mask toetch lower layer(s) to form integrated circuit features. Theseintegrated circuit features may include forming fins or othersemiconductor structures in the layer below the spacers. Thesemiconductor device may be a silicon-on-insulator structure, and thefins may be formed in a silicon on oxide layer below the spacers. Inblock 128, additional processing may include forming field effecttransistors, further etching through lower layers, etc.

Having described preferred embodiments of a device and method for densefinFET SRAM (which are intended to be illustrative and not limiting), itis noted that modifications and variations can be made by personsskilled in the art in light of the above teachings. It is therefore tobe understood that changes may be made in the particular embodimentsdisclosed which are within the scope of the invention as outlined by theappended claims. Having thus described aspects of the invention, withthe details and particularity required by the patent laws, what isclaimed and desired protected by Letters Patent is set forth in theappended claims.

What is claimed is:
 1. A semiconductor device, comprising: a pluralityof fins formed on a semiconductor substrate having a plurality ofpitches; and a plurality of devices formed across two or more of theplurality of fins, the plurality of devices including a first deviceincluding merged fins with an epitaxial material along a majority of asidewall of the merged fins, and a second device including unmergedfins.
 2. The semiconductor device as recited in claim 1, wherein theplurality of devices form an SRAM cell.
 3. The semiconductor device asrecited in claim 1, wherein the first device includes at least one of apull down device and a pass gate device.
 4. The semiconductor device asrecited in claim 1, wherein the second device includes a pull up device.5. The semiconductor device as recited in claim 1, wherein the mergedfins include merged sources and/or drains.
 6. The semiconductor deviceas recited in claim 1, wherein the plurality of pitches includes a firstpitch of 20 nm and a second pitch of 30 nm.